The invention relates to a dispenser for dispensing the contents of cartridges, comprising an advancing mechanism for a piston rod, a housing on which a transmission lever for actuating the advancing mechanism is attached so as to swivel, and a handle, which is affixed to the housing and to which an actuation lever is attached so as to swivel.
Such dispensers are used, for example, in the construction sector to dispense the contents of cartridges that are filled with silicon or other liquid or viscous construction materials. These cartridges normally have a cylindrical body with a dispensing opening in one of the end walls. The opposite end wall is formed by a plunger that can be moved in the cylindrical body, meaning that moving this end wall changes the volume of the cartridge so that the contents of the cartridge can be expelled out of the dispensing opening. The dispenser allows a precise dosing as well as a precise application of the construction material in question. Normally, the dispenser has a piston that is arranged on a piston rod and that can engage with the plunger and force it against the dispensing opening in order to dispense the contents of cartridge. The piston rod is driven by means of an advancing mechanism that is actuated, for example, by a transmission lever that is attached to a housing so as to swivel. This transmission lever is normally coupled to an actuation lever that is attached to a handle, which is affixed to a housing, so as to swivel.
In the case of conventional dispensers, with each stroke of the actuation lever, an essentially constant volume of construction material is dispensed. In this process, in order to dispense the construction material, the operator has to exert a force that is a function of the viscosity of the construction material. With fairly high-viscosity construction materials, this can cause the operator to quickly become fatigued or he might not even be able to exert the requisite dispensing force. In the case of fairly low-viscosity construction materials, however, the requisite dispensing force is low, and many users have expressed the wish to be able to increase the volume of construction material dispensed per stroke.
In order to overcome this drawback of conventional dispensers, European patent specification EP 0 854 760 B1 discloses a generic dispenser with which the operator can use a knob to continuously adjust the transmission ratio between a stroke of the actuation lever and the volume of construction material dispensed. The continuous setting of the transmission ratio by means of a thread, however, is very time-consuming, especially if a switch-over from one end position (e.g. very high-viscosity construction material) to the other end position (e.g. very low-viscosity construction material) has to be carried out. Moreover, such a continuous fine adjustment of the transmission ratio is usually neither desired nor necessary. As a rule, a two-stage (small/large transmission) or three-stage (small/medium/large transmission) setting would be perfectly satisfactory. Furthermore, the devices employed, especially in the construction sector, are often highly stressed, so that the thread soon becomes difficult to adjust due to dirt or corrosion, or in extreme cases, no longer allows any adjustment at all.